.galeria-obras1 {
    width: 50%;
    height: auto;
    display: block;
    margin: 0 0 30px 0; 
    float: left;
}
.galeria-obras1 a span {
    position: absolute;
    top: 10px;
    left: 3%;
    padding: 5px;
    background: #dd1b1b00;
    color: #fff0;
    font-weight: bold;
    border-radius: 3px;
}
.galeria-obras2 {
    width: 50%;
    height: auto;
    display: block;
    margin: 0 0 30px 0; 
    float: left;
}
.galeria-obras2 a span {
    position: absolute;
    top: 10px;
    left: 51%;
    padding: 5px;
    background: #dd1b1b00;
    color: #fff0;
    font-weight: bold;
    border-radius: 3px;
}